1. Field of the Invention:
This invention relates, in general, to electrical inductive apparatus and, more specifically, to single-phase power transformers with magnetic shielding cores.
2. Description of the Prior Art:
Large shell-form power transformers have usually required shields constructed of magnetic laminations located around the transformer tank to prevent excessive heating in the metallic tank members. U.S. Pat. No. 3,821,677, which is assigned to the assignee of this invention, describes a shielding arrangement of this type as applied to a three-phase transformer. Several arrangements have been developed to reduce the heating in the tank walls which do not rely upon the placement of shielding laminations along the tank structure. U.S. Pat. No. 3,571,772, which is assigned to the assignee of this invention, discloses an arrangement wherein shielding magnetic core loops are located on each side of the main magnetic core of a single-phase transformer. The shielding loops not only direct much of the leakage flux away from the tank walls, but also function with the main core to provide a portion of the primary magnetic flux path linking the various windings. This allows some reduction in the size of the magnetic core and of the tank enclosure.
The arrangement disclosed in U.S. Pat. No. 3,571,772 is useful in power transformers having moderately high ratings. However, certain problems arise when the rating of the transformer is extremely high. In very large single-phase transformers, the main magnetic core becomes so thick that proper heat dissipation is difficult to obtain and hot spots near the center of the lamination punchings may develop. In addition, the mere size and weight of the main magnetic core structure is such that conventional supporting arrangements are insufficient to hold the laminations properly.
U.S. Pat. No. 2,780,786 discloses a magnetic core arrangement which uses shielding loops and which has a passageway or duct in the main core for the purpose of ventilating the magnetic core structure. However, the magnetic core arrangement of the transformer disclosed in U.S. Pat. No. 2,780,786 is intended for use with the faces of the magnetic laminations mounted perpendicular to the horizontal mounting surface. With this orientation, the weight of the laminations does not act perpendicular to the lamination faces. Thus, supporting arrangements used for the core of U.S. Pat. No. 2,780,786 are basically different that those used for supporting shell-form magnetic cores wherein the lamination faces are parallel to a horizontal plane.
Therefore, it is desirable, and it is an object of this invention, to provide a shielded shell-form power transformer wherein the magnetic core is constructed to provide adequate cooling for internal core portions and wherein the horizontally oriented laminations are conveniently supported.